1. Field of the Invention
The field of the present invention is internal combustion engines of a type having a valve operating system connected to a pair of intake valves and arranged to open one of the intake valves only in a very small amount such that the one intake valve is brought into its substantially inoperative state, in a suction stroke mainly in a low speed rotation region of the engine, a fuel injection valve capable of injecting fuel toward a pair of intake ports independently corresponding to the intake valves, and a control means for controlling the operation of the fuel injection valve.
2. Description of the Prior Art
A conventional internal combustion engine is disclosed, for example, in Japanese Utility Model Application Laid-open No. 195913/85, wherein one of a pair of intake valves is lifted only in a very small amount in a low speed operation region of the engine, thereby preventing an increase in fuel consumption and avoiding a deposit of fuel remaining in an intake port in a substantially inoperative state to provide a stable combustion in the low speed operation region of the engine.
If the one intake valve is brought into a substantially inoperative state as in the prior art, it is possible to form a swirl within a combustion chamber by flowing of an air-fuel mixture into the combustion chamber substantially only through the other intake valve. It is conventionally known that combustibility is improved by providing an axially stratified air charge or supply wherein the concentration of fuel is varied in an axial direction in the combustion chamber to form a rich zone of a relative high concentration of fuel around a spark plug. Thus, it is believed that a combination of the swirl formation with the axially stratified air charge provides a further improved combustibility to enable stable combustion of a dilute or lean air-fuel mixture.
On the other hand, it has been definitely shown by experiments made by the present inventors that in an operational condition in which one of the intake valves is substantially in an inoperative state, an axially stratified air charge is possible only when a time of injection of fuel by the fuel injection valve is a particular time.